Smoke Detection in Stationary Video Using Wavelets Helmut Knaust Department of Mathematical Sciences The University of Texas at El Paso El Paso TX 79968-0514 hknaust@utep.edu January 6, 2012
The Problem The Problem: VIDEO:
Fire/Smoke Detection Techniques Standard techniques for fire or smoke detection: Indoor smoke detectors ionization photoelectric air-sampling CO or CO 2 sensors Infra-red sensors/cameras
Fire/Smoke Detection Techniques Techniques for fire/smoke detection with stationary video: Fourier analysis - using the flickering of flames Luminance/chrominance energy measurements (for color videos) A wavelet technique - high frequency energy measurements
Prerequisites Prerequisites for students are quite minimal: Basics of Digital Signal Processing Some knowledge of the basic wavelet transforms and their application to digital images Familiarity with Mathematica or MatLab
Student Outcomes Expected Student Outcomes: Students will get a flavor of the ideas and issues involved in applying mathematics to a relevant engineering problem. Students will develop a deeper understanding of wavelet transforms and their applications. Students will improve their programming skills.
Theory Each pixel in a gray-scale image is represented by an integer between 0 and 255 = 2 8 1 (8 bit = 1 byte) 0=black, 255=white
Introduction Luminance and Chrominance High Frequency Content References Theory A color image consists of three color channels: Red, Green and Blue R G B
Introduction Luminance and Chrominance High Frequency Content References Theory The Red, Green and Blue color channels can be thought of as grayscale images: R G B
Introduction Luminance and Chrominance High Frequency Content References Theory For many applications it is more useful to split the color information into a luminance channel (Y) and two chrominance channels (Cb and Cr) instead: Y Cb Cr
Theory Energy is a measurement of the brightness of a grayscale image. For a matrix A = (a ij ), its energy E(A) is defined as E(A) = i aij 2. (This is just the square of the 2-norm of A.) A brighter image will have higher energy than a darker one. j
Application Smoke Detection Idea #1: Smoke makes an image grayer and less colorful. Thus an increase in the ratio between the energy of the luminance channel and the combined energy of the chrominance channels should be an indicator for the presence of smoke.
Application VIDEO: Luminance vs. Chrominance Energy Ratio:
Theory Our next technique works for grayscale videos. In case of a color video, we will use its luminance channel. Wavelet transforms separate the low-frequency content of an image from the high-frequency content.
Applications Smoke Detection Idea #2: Smoke obscures edges. Thus a decrease in the combined energy of the high-frequency portions of an image should be an indicator for the presence of smoke. (Note that this will detect smoke only if edges are present.)
Applications VIDEO: High-frequency Energy:
Applications This technique can be refined to identify smoke regions within the video images. 1 Each image is partitioned into sub-images of size 8 8 pixels each.
Applications 2 The wavelet transform is computed for each sub-image. 3 The energy of the high-frequency portions is computed for each sub-image. 4 The first (smoke-less) frame of the video is now used as a reference frame.
Applications 5 The energies computed are subtracted from the corresponding energy values of the reference frame. 6 The result is visualized. If the high-frequency energy of a region decreases, a positive value will result in Step 5, leading to a bright pixel. If the high-frequency energy of a region increases or remains unchanged, a non-positive value is computed in Step 5, leading to a black pixel.
Applications VIDEO: High-frequency Energy:
References B. Ugur Toreyin, Yigithan Dedeoglu & A. Enis Cetin: Contour Based Smoke Detection In Video Using Wavelets. Proceedings of the 14th European Signal Processing Conference (EUSIPCO 2006). Videos: http://signal.ee.bilkent.edu.tr/visifire/demo/sampleclips.html Video frame extraction program: VirtualDub-1.9.11